The present invention relates to a film easily soluble in cold water and more specifically to a film easily soluble in cold water, which comprises a water-soluble polymer obtained by saponifying a copolymer of an allyl ester and a vinyl ester and which is suitable for, in particular preparing a package which can directly be thrown into water.
Recently, water-soluble films have been used as packaging materials. In particular, they have been used for packaging water-soluble or water-dispersible solid materials, which are toxic to the user, which must be correctly dispensed upon employing the same, and/or which are difficult to remove from human body when they are attached thereto. As such solid materials, there may be mentioned, for instance, fine powdery water-soluble or water-dispersible materials such products for cleaning as detergents and bleaching agents; such agrochemicals as herbicides, insecticides, fungicides, antifungals and antiseptics; pigments and dyes. In this respect, such a fine powdery material is wrapped with a water-soluble film and then the wrapped material is in general added to water as it is without taking off the film. Therefore, it is required that the film for packaging should be dissolved therein within a short period of time to thereby dissolve and disperse the fine powdery material into water. This in turn requires that the film used for wrapping the material should be easily soluble in cold water.
To date, polyvinyl alcohol (hereinafter referred to as "PVA" for simplicity) has been used as a material for forming such a water-soluble film. In this connection, the completely saponified PVA is hardly soluble in cold water and, therefore, PVA partially saponified has been used for such a purpose. The partially saponified PVA is certainly easily soluble in cold water, but it undergoes additional saponification when it brings into contact with any alkaline material, which leads to the lowering of stability with time. In particular, it becomes hardly soluble in cold water with the lapse of time, for instance, 2 to 3 weeks later.
Recently, there has been proposed a method in which PVA is modified with an unsaturated carboxylic acid in order to eliminate the aforementioned disadvantage and water-soluble films prepared from such modified PVA have been put on the market. In this respect, reference is made to "Suiyosei Kobunshi No Oyo To Shijyo (The Application of Water-Soluble Polymers and the Market Therefore)", pp. 266-277, published by CMC Co.
The cold water-solubility of a film comprised of PVA modified with unsaturated carboxylic acids is not influenced even when it is brought into contact with an alkaline material. On the contrary, the solubility of the film in cold water in greatly influenced by acidic material.